This research exploits the cardiac ganglion of crabs and lobsters to study endogenous neuronal properties, their biophysical bases, the mechanisms by which they are modified and controlled by synaptic interactions, both electronically and chemically mediated, mechanisms of integration, and the mode of action on an integrating neural system of a peptide neurohormone. The ganglion exhibits spontaneity, stable rhythmicity and burst impulse firing. With 9 neurons, it is the smallest neural system that can be isolated functionally intact which exhibits major features of central nervous system functioning. Electrophysiological techniques employing several intracellular and extracellular electrodes simultaneously will be used. They permit monitoring of all impulse traffic, evaluation of synaptic interactions and recording of endogenously generated potential changes such as pacemaker (PMP) and burst forming or 'driver' potentials (DP). The characterization of DPs, isolated in the soma and initial segment by ligaturing, will be extended with voltage clamping techniques. Functional isolation and biophysical characterization of PMPs will be undertaken. The observations will be extended with intracellular recording from the small cells, recently found to be possible in the local crab, Portunus sanguinolentus. Functional and electron microscopical (EM) localization of the sites of PMP and DP generation will be made with extracellular microelectrodes. To analyze endogenous potentials and the modification of them by neural interactions, chemically mediated synaptic transmission will be pharmacologically blocked. A technique will be sought to 'decouple' the electrotonic junctions; effects will be correlated with EM observable changes. The two cardioactive peptide hormones, as well as the amines, of crab pericardial organs will be separately tested and their mode of action in changing burst rate, duration, and coordination analyzed. Knowledge gained from study of this model system may be expected to contribute and have general relevance to basic understanding of CNS functioning.